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Summary
In Episode 3 of Retrofitting Our Reality, Rebecca Stewart speaks with Faraby Farid about how heritage buildings can be adapted for modern use while remaining fit for the long term. From building fabric and thermal comfort to capital cost, resilience and the wider city context, Faraby shows how early design decisions shape building performance long before plant is specified.
In this live sketch session, the conversation explores what it really takes to retrofit historic buildings for the next century, reducing loads through better fabric, thinking beyond upfront cost and recognising that building performance is increasingly influenced by the climate and infrastructure.
Designing heritage buildings for the next 100 years: key themes
Key themes at a glance:
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Fabric first | Performance starts with the building before the system
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Comfort and control | Why user experience still matters
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Beyond capital cost | Resilience, regulation and long-term value
- Thinking at city scale | How wider urban conditions are shaping building decisions
Faraby looks at retrofit from a practical perspective, focusing on real challenges like working with heritage fabric, limited space, comfort, cost and resilience. The discussion highlights how the choices made early in the design process set the direction for everything that comes next.
The episode also looks beyond the building itself. As cities get hotter and the need for cooling increases, issues like solar gain, infrastructure and shared energy systems are becoming more important. This leads to a wider view of retrofit, linking how individual buildings perform to the wider conditions and challenges of the city.
“We have to think beyond the building and start thinking at city scale.”
FAraby FArid
Technical Lead for Real Estate Developments and Energy Strategy
Designing heritage buildings for the next 100 years episode:
Places + projects
- Regent Street / West End heritage buildings (London)
- 8 Bishopsgate (London)
- Qatar National Museum (Qatar)
- Paris district cooling network
- Hilson Moran Living Lab, 80 Charlotte Street (filming location)
Organisations
- The Crown Estate
- Arup
- Hilson Moran (Living Lab filming location)
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Vertical Meadows
-
Attain
- Artus Air
Building fabric + retrofit strategies
- Fabric-first design approach
- Secondary glazing vs vacuum-insulated glazing
- Internal vs external insulation trade-offs
- Airtightness and air leakage reduction
- Solar gain and façade response
- Mixed-mode vs sealed façade strategies
Systems + infrastructure
- Heat pumps (air / water-based systems)
- VRF (variable refrigerant flow) systems
- Water-based HVAC systems
- Thermal storage (including phase change materials)
- Basement plant strategies
- District heating and cooling networks
- Refrigerant phase-down (F-Gas implications)
City-scale + environmental context
- Urban heat island effect
- London heat mapping / microclimate variation
- District energy at city scale
- Paris district cooling precedent
- Electrification of heat and cooling demand
- Infrastructure-led decarbonisation
Human factors + design thinking
- Occupant comfort vs energy use
- Perceived control (windows, airflow, temperature)
- Long-term building usability
- Balancing feasibility, viability and desirability
- Retrofitting for buildings with 100+ year lifespans
- Designing for real-world performance, not just compliance
Delivery + industry challenges
- Capital cost vs whole-life value
- Net lettable area vs performance trade-offs
- Programme pressure in retrofit
- Industry risk aversion and standard solutions
- Coordination across multiple buildings and timelines
- Future-proofing for district energy connection
Transcript
*Transcript edited lightly for clarity while preserving the original meaning and tone.
Rebecca Stewart:
Welcome to Retrofitting Our Reality, a podcast brought to you by Artus Air. I’m Rebecca Stewart, CEO and co-founder of Artus Air, and it’s my pleasure today to be joined by someone who is shaping how we think about the future of existing buildings.
Welcome to Retrofitting Our Reality, a podcast brought to you by Artus Air. I’m Rebecca Stewart, CEO and co-founder of Artus Air, and it’s my pleasure today to be joined by someone who is shaping how we think about the future of existing buildings.
Faraby, thank you for joining us. Please introduce yourself to our listeners.
Faraby Farid:
Thank you, Rebecca. I’m Faraby Farid, Technical Lead for Real Estate Developments and Energy Strategy at The Crown Estate.
Thank you, Rebecca. I’m Faraby Farid, Technical Lead for Real Estate Developments and Energy Strategy at The Crown Estate.
My background is in mechanical engineering. I’ve been designing buildings for close to two decades now. I started my career at Arup, where I worked on projects including the Qatar National Museum, which was a very iconic building in the middle of the desert. That was really where my sustainability mindset came in, because the question was how to make something sustainable in a place where that feels very difficult.
I then worked on a number of other projects and, before joining The Crown Estate, I worked on 8 Bishopsgate from start to finish, which became the UK’s first BREEAM Outstanding tall building.
Every project teaches you something, but one of the biggest things I learned is that if you think outside the box and do something differently, you can achieve better outcomes.
The reason I moved to The Crown Estate was that, by the time I was working on my second 50-storey building, I realised I was still having the same conversations I had been having ten years earlier on 8 Bishopsgate. I started thinking: instead of influencing one project at a time, how can I influence a whole part of a city?
That opportunity came up at The Crown Estate, so I made the move. For me, it is all about sustainability, keeping assets alive for as long as possible, and creating the best quality spaces.
Rebecca Stewart:
And joining us today as well is Roger Olsen, who is here to co-sketch with Faraby. Roger, thank you for coming in. Please introduce yourself to our listeners.
And joining us today as well is Roger Olsen, who is here to co-sketch with Faraby. Roger, thank you for coming in. Please introduce yourself to our listeners.
Roger Olsen:
I’m Roger Olsen. I have always been fascinated by innovation, ever since university. I joined Arup many years ago as a mechanical engineer designing buildings, but I was always passionate about innovation, which is really why Faraby and I are in the same slightly crazy box.
I’m Roger Olsen. I have always been fascinated by innovation, ever since university. I joined Arup many years ago as a mechanical engineer designing buildings, but I was always passionate about innovation, which is really why Faraby and I are in the same slightly crazy box.
You have to move things forward.
Rebecca Stewart:
Essentially, yes.
Essentially, yes.
Roger Olsen:
Exactly. You have to move things forward, and we share that same passion.
Exactly. You have to move things forward, and we share that same passion.
Rebecca Stewart:
The reason I’ve asked you both to join me today is because I love the way you work together and build on ideas together. So we’re going to do a sketch session today.
The reason I’ve asked you both to join me today is because I love the way you work together and build on ideas together. So we’re going to do a sketch session today.
Faraby, you’ve brought us a problem. We’re going to start with that problem and, within 30 minutes, see how far we can get in solving it.
Roger Olsen:
How hard can it be?
How hard can it be?
Rebecca Stewart:
Faraby, introduce the problem for us.
Faraby, introduce the problem for us.
Faraby Farid:
If you walk around central London, particularly in the West End, you see beautiful old buildings like this. They have been standing for hundreds of years and they need to stand for hundreds of years to come.
If you walk around central London, particularly in the West End, you see beautiful old buildings like this. They have been standing for hundreds of years and they need to stand for hundreds of years to come.
But inside, they are not always great spaces. They were not designed for the uses we have now. The fabric is not built for purpose. It leaks heat throughout the year. It is often difficult to ventilate properly. The services strategy is constrained. And yet we now expect these buildings to meet modern standards for comfort, performance and sustainability.
Rebecca Stewart:
So we are looking at a building that is valuable and has longevity, but it was not designed for modern occupation.
So we are looking at a building that is valuable and has longevity, but it was not designed for modern occupation.
Faraby Farid:
Exactly. The challenge is how to adapt it in a way that improves performance while respecting what is already there.
Exactly. The challenge is how to adapt it in a way that improves performance while respecting what is already there.
Roger Olsen:
And that is where you have to start with the building itself. Before you start thinking about systems, you need to understand what the fabric is doing, what the constraints are, and what opportunities there might be to reduce demand before adding plant.
And that is where you have to start with the building itself. Before you start thinking about systems, you need to understand what the fabric is doing, what the constraints are, and what opportunities there might be to reduce demand before adding plant.
Rebecca Stewart:
So when you approach a building like this, what are the first things you look at?
So when you approach a building like this, what are the first things you look at?
Faraby Farid:
You start with the building envelope. How much glazing is there? What is the condition of the façade? Where are the heat losses? What is the solar gain? What are the planning constraints? What can you touch and what can you not touch?
You start with the building envelope. How much glazing is there? What is the condition of the façade? Where are the heat losses? What is the solar gain? What are the planning constraints? What can you touch and what can you not touch?
In heritage buildings, there are often trade-offs. You might be considering secondary glazing or vacuum-insulated panels. You might be looking at internal insulation versus external insulation. You might be asking how much natural ventilation is realistically possible in a busy urban environment affected by noise and pollution.
Those are the kinds of early decisions that set the direction for everything else.
Roger Olsen:
Let me sketch that out.
Let me sketch that out.
If I draw a simple section through the building, here’s the street level, here’s the building, and here are the occupied floors. When these buildings were first built, they would have relied heavily on natural ventilation through open windows.
Today, that is much harder. We have buses, traffic, noise, pollution. In future, that might improve if we pedestrianise more streets or move fully to electric vehicles, but at the moment it is a real constraint.
So what often happens is that you end up with a more sealed façade. The windows may technically open, but in practice people are less likely to use them, or the conditions outside are not suitable. That leads you into a mixed-mode or sealed-building conversation, and each of those choices has consequences.
Rebecca Stewart:
So even the question of whether a window opens is no longer simple.
So even the question of whether a window opens is no longer simple.
Faraby Farid:
No, exactly. One of the things we have found while looking at mixed mode is that you also need to ask whether the additional embodied carbon involved in creating an openable window is worth it over the long term.
No, exactly. One of the things we have found while looking at mixed mode is that you also need to ask whether the additional embodied carbon involved in creating an openable window is worth it over the long term.
Rebecca Stewart:
So that means more material in the frame, the locking system, the opener?
So that means more material in the frame, the locking system, the opener?
Faraby Farid:
Yes. If it is a proper mixed-mode system, especially if it is automated, there is more material involved. So then you are balancing embodied carbon, operational performance, comfort and usability.
Yes. If it is a proper mixed-mode system, especially if it is automated, there is more material involved. So then you are balancing embodied carbon, operational performance, comfort and usability.
That is why retrofit is rarely straightforward. You are not just asking one question. You are asking several at the same time.
Rebecca Stewart:
And comfort clearly sits right at the centre of this.
And comfort clearly sits right at the centre of this.
Roger Olsen:
It does. Comfort is not just about temperature. It is also about control, airflow, noise and how people experience the space.
It does. Comfort is not just about temperature. It is also about control, airflow, noise and how people experience the space.
Even if occupants rarely use the control in practice, the ability to open a window or adjust your immediate environment can make people feel more comfortable and more satisfied with a building.
Faraby Farid:
Yes, and that matters. We can sometimes get overly focused on pure energy metrics, but buildings are for people. If a building is meant to last for centuries, it has to continue working for the people using it as well as for the carbon targets we are trying to meet.
Yes, and that matters. We can sometimes get overly focused on pure energy metrics, but buildings are for people. If a building is meant to last for centuries, it has to continue working for the people using it as well as for the carbon targets we are trying to meet.
Rebecca Stewart:
So if you improve the fabric first, what does that change downstream?
So if you improve the fabric first, what does that change downstream?
Roger Olsen:
It changes a lot. A stronger building fabric reduces peak loads, so systems can be sized for more normal operating conditions rather than extremes. That can mean smaller systems, lower operational demand, more comfortable spaces and better protection of valuable floor area.
It changes a lot. A stronger building fabric reduces peak loads, so systems can be sized for more normal operating conditions rather than extremes. That can mean smaller systems, lower operational demand, more comfortable spaces and better protection of valuable floor area.
In retrofit projects, that difference can determine whether large plant rooms or extensive ductwork are needed at all.
Faraby Farid:
Exactly. In practice, fabric decisions often determine whether large mechanical systems are needed at all.
Exactly. In practice, fabric decisions often determine whether large mechanical systems are needed at all.
Roger Olsen:
If we sketch the façade in a bit more detail, what we often find in these heritage buildings is a single-glazed window set within a very old wall construction. There is usually no insulation in the wall, and the window performance is poor by modern standards.
If we sketch the façade in a bit more detail, what we often find in these heritage buildings is a single-glazed window set within a very old wall construction. There is usually no insulation in the wall, and the window performance is poor by modern standards.
So the obvious question is: what can you do about that? One traditional answer is secondary glazing, but that comes with drawbacks.
Faraby Farid:
Yes. The most common traditional response is to put a secondary glazing system in. But what that does is lose area internally, and it can also create problems with condensation between the new glazing line and the original single-glazed line.
Yes. The most common traditional response is to put a secondary glazing system in. But what that does is lose area internally, and it can also create problems with condensation between the new glazing line and the original single-glazed line.
So it is not necessarily something we should just continue doing as standard. We should be looking at what else is possible in the market.
Rebecca Stewart:
So what is the better option?
So what is the better option?
Faraby Farid:
One of the more interesting solutions is vacuum-insulated glass. It is roughly the same thickness as a single-glazed pane, which is often what you find in heritage buildings, but it can deliver something much closer to double-glazing performance.
One of the more interesting solutions is vacuum-insulated glass. It is roughly the same thickness as a single-glazed pane, which is often what you find in heritage buildings, but it can deliver something much closer to double-glazing performance.
The challenge is cost. That is one reason uptake has been slower. But before you even get to the glass itself, you also need to solve the air leakage around the frame. Otherwise, you are not dealing with the full problem.
Roger Olsen:
And when we say leakage, we mean air leakage through the façade, not water. That is an important distinction, because air leakage can be a major driver of poor performance.
And when we say leakage, we mean air leakage through the façade, not water. That is an important distinction, because air leakage can be a major driver of poor performance.
Rebecca Stewart:
Can I just ask something there? You said vacuum-insulated glass is more expensive, but you have also said that some of the traditional approaches reduce net lettable area. So there must be a trade-off here.
Can I just ask something there? You said vacuum-insulated glass is more expensive, but you have also said that some of the traditional approaches reduce net lettable area. So there must be a trade-off here.
Faraby Farid:
Exactly. Traditional cost appraisal does not always look at it that way, and that is part of the issue.
Exactly. Traditional cost appraisal does not always look at it that way, and that is part of the issue.
You need to weigh up the development cost against the lifetime energy saving and also the revenue impact of preserving more lettable space. At The Crown Estate, because we hold assets for the long term, we can look at both development and operation together. That makes a big difference.
We need to compare the usual solution against the alternative in terms of cost, carbon and net lettable implications, all on the same basis, and then make the decision from there.
Rebecca Stewart:
That must be quite unusual.
That must be quite unusual.
Faraby Farid:
It probably is. We hold our assets for the long term, potentially forever, so the view is different.
It probably is. We hold our assets for the long term, potentially forever, so the view is different.
I do think the market is changing and developers are bringing in more technical insight, but generally they do not have a full engineering team looking across all their assets in that way. That is something we are trying to change.
Rebecca Stewart:
And presumably, by showing that it can be done, you help give others confidence.
And presumably, by showing that it can be done, you help give others confidence.
Roger Olsen:
Yes, absolutely. If a client can see that it works on a challenging building, then it gives reassurance. It prompts the rest of the industry. It shows that the costs can stack up and that it is not just a theoretical exercise.
Yes, absolutely. If a client can see that it works on a challenging building, then it gives reassurance. It prompts the rest of the industry. It shows that the costs can stack up and that it is not just a theoretical exercise.
And once something starts being used more widely, costs can come down. Volume helps.
Faraby Farid:
That is exactly what we are hoping for. If we start rolling out these approaches on our estate, then a broader market develops and others can pick them up too.
That is exactly what we are hoping for. If we start rolling out these approaches on our estate, then a broader market develops and others can pick them up too.
Roger Olsen:
The other classic question is insulation.
The other classic question is insulation.
If you are thinking in purely technical terms, the best place for insulation is often on the outside of the wall, because that keeps the structure warm and dry and protects the fabric. But of course, if you applied that logic literally to somewhere like Regent Street, the appearance would be completely transformed, and not in a good way.
So in practice, the challenge is usually how much insulation you can add internally without encroaching too much on the usable space.
Rebecca Stewart:
So again there is a trade-off.
So again there is a trade-off.
Faraby Farid:
Yes. There are higher-performance insulation products that do not take up as much space, but again they tend to be more expensive than the usual approach.
Yes. There are higher-performance insulation products that do not take up as much space, but again they tend to be more expensive than the usual approach.
What I have been pushing for since joining The Crown Estate is for our consultants, design teams and quantity surveyors to think differently. Rather than saying, “That is too expensive, so we would not do it,” we need the implications set out properly: cost, carbon and net lettable space all considered together.
Then you can make a much more informed decision.
Rebecca Stewart:
It would be nice to think that the lessons being learned in this kind of top-tier estate can also be applied more widely.
It would be nice to think that the lessons being learned in this kind of top-tier estate can also be applied more widely.
Faraby Farid:
That is absolutely the hope. One of The Crown Estate’s broader goals is prosperity for the nation. If we can help innovate the market and bring costs down on these kinds of solutions, then that helps the wider market too.
That is absolutely the hope. One of The Crown Estate’s broader goals is prosperity for the nation. If we can help innovate the market and bring costs down on these kinds of solutions, then that helps the wider market too.
Rebecca Stewart:
And how do you pass that learning on?
And how do you pass that learning on?
Faraby Farid:
By doing things like this. By sharing what we have learned, turning it into case studies, writing about it, putting it on LinkedIn, being open about the process.
By doing things like this. By sharing what we have learned, turning it into case studies, writing about it, putting it on LinkedIn, being open about the process.
We need to share knowledge much more across the industry. Construction is very change-averse. Contractors do not always like doing things differently. Consultants can be nervous about pushback. So if innovation is made more visible, people become more comfortable trying new approaches.
Rebecca Stewart:
That is quite a position to be in, though — being able to show part of the way, try things, learn from what works and what does not.
That is quite a position to be in, though — being able to show part of the way, try things, learn from what works and what does not.
Faraby Farid:
Yes, and that matters, because otherwise we just repeat the same answers again and again.
Yes, and that matters, because otherwise we just repeat the same answers again and again.
Roger Olsen:
So if we move on from the close-up of the façade to a wider section through the building, the next question is ventilation and conditioning.
So if we move on from the close-up of the façade to a wider section through the building, the next question is ventilation and conditioning.
Originally, these buildings would have relied on natural ventilation through open windows. Today, because of traffic, noise and pollution, that does not really work in the same way.
In future, some of that external environment may improve if streets are pedestrianised or vehicles become quieter and cleaner, but it will not completely solve the problem. So you often end up with something closer to a sealed façade, or at least a more controlled mixed-mode approach.
Rebecca Stewart:
So the windows may technically open, but in practice the building behaves differently.
So the windows may technically open, but in practice the building behaves differently.
Roger Olsen:
Exactly. You might be able to open them at the right time of year, if conditions allow, but then you are relying on people to use them appropriately, and comfort becomes more variable.
Exactly. You might be able to open them at the right time of year, if conditions allow, but then you are relying on people to use them appropriately, and comfort becomes more variable.
Faraby Farid:
And there is another question there too, which is whether the additional embodied carbon in a truly openable, automated mixed-mode façade is worth it over the long term.
And there is another question there too, which is whether the additional embodied carbon in a truly openable, automated mixed-mode façade is worth it over the long term.
If it is a proper mixed-mode system, there are more materials involved, more controls, more actuators, more complexity.
Rebecca Stewart:
And yet people still care about having control.
And yet people still care about having control.
Faraby Farid:
Very much so. If you give occupants the feeling of control, they feel better in a space. Even if they do not actually use that control very much, the fact that they feel they can often results in fewer complaints.
Very much so. If you give occupants the feeling of control, they feel better in a space. Even if they do not actually use that control very much, the fact that they feel they can often results in fewer complaints.
That is something we are learning more and more. Comfort is not just technical. There is a psychological dimension to it as well.
Roger Olsen:
So once you have looked at the fabric, the next question is where the heating and cooling are coming from, and how you do that in the most energy-efficient way.
So once you have looked at the fabric, the next question is where the heating and cooling are coming from, and how you do that in the most energy-efficient way.
The traditional approach is to have plant on the roof — big boxes sitting on top of the building doing the heating and cooling. But that is not always attractive from a visual point of view, and it also takes up a lot of space.
Rebecca Stewart:
And that has an impact on the building elevation too, doesn’t it? It is not just a technical issue.
And that has an impact on the building elevation too, doesn’t it? It is not just a technical issue.
Roger Olsen:
Exactly. It affects the architecture and the appearance of the building. And plant space is not small. It can easily be something like eight per cent of the floor area being served, which is a lot when you think about how valuable roof and floor space are in a city-centre building.
Exactly. It affects the architecture and the appearance of the building. And plant space is not small. It can easily be something like eight per cent of the floor area being served, which is a lot when you think about how valuable roof and floor space are in a city-centre building.
Faraby Farid:
And if we are trying to avoid gas-based systems and move to heat pumps, those systems can take up even more space. A heat pump can take up a full floor height, and if you cannot fit it on the roof, you may have to put it somewhere else in the building, which could mean losing a whole floor of lettable area.
And if we are trying to avoid gas-based systems and move to heat pumps, those systems can take up even more space. A heat pump can take up a full floor height, and if you cannot fit it on the roof, you may have to put it somewhere else in the building, which could mean losing a whole floor of lettable area.
So the challenge becomes: how do you avoid that?
Roger Olsen:
And this is where the next cunning plan comes in.
And this is where the next cunning plan comes in.
Instead of relying entirely on large roof plant, you start thinking about whether the energy source can be handled differently. For example, can you use the basement? Can you use storage? Can you reduce the peak demand that the plant has to serve?
Faraby Farid:
Yes. A lot of these heritage buildings do have basements, even if they are not especially useful in the normal commercial sense because the height is constrained or the access is awkward.
Yes. A lot of these heritage buildings do have basements, even if they are not especially useful in the normal commercial sense because the height is constrained or the access is awkward.
But those spaces can be useful for plant and storage. For example, you can use the basement for a thermal store.
If you fill that space with stored water or another storage medium, you can reduce the size of the heat pump you need because you are no longer sizing it purely for peak load. You can size it more for nominal demand, then let the thermal store absorb the peaks.
Rebecca Stewart:
So instead of designing for the hottest day of the year, you are designing for the normal operating condition.
So instead of designing for the hottest day of the year, you are designing for the normal operating condition.
Faraby Farid:
Exactly. Instead of designing for that 40-degree day that might happen only a few times, you size for normal conditions and let the thermal store help manage the difference.
Exactly. Instead of designing for that 40-degree day that might happen only a few times, you size for normal conditions and let the thermal store help manage the difference.
That means the plant can be smaller.
Rebecca Stewart:
And you have seen that work commercially?
And you have seen that work commercially?
Faraby Farid:
Yes, there are examples where that works, and you can go even further with phase change materials in the store.
Yes, there are examples where that works, and you can go even further with phase change materials in the store.
Rebecca Stewart:
What does that do?
What does that do?
Faraby Farid:
It reduces the volume required for the storage, because phase change materials can store more energy in a relatively small space.
It reduces the volume required for the storage, because phase change materials can store more energy in a relatively small space.
Roger Olsen:
Yes. It is a bit like the difference between just storing cool water and storing something that also goes through a change of state, like melting or freezing. You get a lot of energy transfer for a relatively small volume, which makes the basement solution much more efficient.
Yes. It is a bit like the difference between just storing cool water and storing something that also goes through a change of state, like melting or freezing. You get a lot of energy transfer for a relatively small volume, which makes the basement solution much more efficient.
Rebecca Stewart:
So you are trying to maximise the use of the basement for thermal storage and plant, and minimise the amount of visible plant on the roof.
So you are trying to maximise the use of the basement for thermal storage and plant, and minimise the amount of visible plant on the roof.
Faraby Farid:
Exactly. If we can maximise what happens in the basement, then the roof becomes less dominated by mechanical plant and more available for other uses.
Exactly. If we can maximise what happens in the basement, then the roof becomes less dominated by mechanical plant and more available for other uses.
And that matters, because the roof can become a genuinely valuable space — for greenery, biodiversity, amenity and just better quality urban environments.
Roger Olsen:
Yes. If you can get rid of as much mechanical plant as possible from the roof, then suddenly you have the opportunity for a proper green roof.
Yes. If you can get rid of as much mechanical plant as possible from the roof, then suddenly you have the opportunity for a proper green roof.
And a green roof is not just a nice extra. It is useful from an amenity point of view, from a biodiversity point of view and from a city-scale climate point of view.
Rebecca Stewart:
Do you have examples of that in practice?
Do you have examples of that in practice?
Faraby Farid:
At The Crown Estate, every new development we are doing includes green roofs. We are also using vertical meadows during construction as a meanwhile-use strategy and on hoardings.
At The Crown Estate, every new development we are doing includes green roofs. We are also using vertical meadows during construction as a meanwhile-use strategy and on hoardings.
So that thinking is very much already there. And part of the longer-term ambition is to create connected green corridors across the estate — linking different green spaces together in a way that benefits nature as well as people.
Roger Olsen:
And that is really important. If you look at the city as a whole, small pieces of greenery work much better when they connect to each other. Bees, birds and other species need those linked spaces.
And that is really important. If you look at the city as a whole, small pieces of greenery work much better when they connect to each other. Bees, birds and other species need those linked spaces.
So if you can connect green roofs and roof gardens, even in relatively modest ways, you can create a much more meaningful ecological corridor.
Faraby Farid:
Yes. It is part of that wider vision of reconnecting landscapes and public space. And one way to help make that possible is to remove as much mechanical plant from the roof as you can.
Yes. It is part of that wider vision of reconnecting landscapes and public space. And one way to help make that possible is to remove as much mechanical plant from the roof as you can.
Which brings us to district energy.
Rebecca Stewart:
This is where you start thinking beyond the individual building.
This is where you start thinking beyond the individual building.
Faraby Farid:
Exactly. I am a big proponent of district energy networks because, if they are designed properly, they allow you to remove a lot of duplicated plant from individual buildings.
Exactly. I am a big proponent of district energy networks because, if they are designed properly, they allow you to remove a lot of duplicated plant from individual buildings.
You still need the plant somewhere, of course, but it does not have to be in every building. If you have a contiguous estate and a long-term view, you can make different decisions. You can accept that one or two buildings might host the main plant in order to benefit twenty other buildings.
That is only really possible when you are thinking at estate scale or city scale, rather than building by building.
Rebecca Stewart:
And that changes the roof strategy completely.
And that changes the roof strategy completely.
Faraby Farid:
Yes. Suddenly, buildings whose roofs are valuable for amenity, biodiversity or architectural reasons do not need to carry all that plant.
Yes. Suddenly, buildings whose roofs are valuable for amenity, biodiversity or architectural reasons do not need to carry all that plant.
Instead, the heating and cooling can come through shared infrastructure. And because the network is serving multiple buildings, you do not need to size everything for the peak load of every building individually.
Roger Olsen:
That is one of the big efficiency benefits. If every building has its own system, each one is sized for its own maximum requirement. But if you join several buildings together, the total system can be sized closer to the nominal combined load, because not every building peaks at exactly the same time.
That is one of the big efficiency benefits. If every building has its own system, each one is sized for its own maximum requirement. But if you join several buildings together, the total system can be sized closer to the nominal combined load, because not every building peaks at exactly the same time.
So instead of five separate peak-sized systems, you might only need the equivalent of three. That means less equipment overall, lower embodied carbon in the plant, and more efficient operation.
Rebecca Stewart:
And operationally, it is more dynamic as well.
And operationally, it is more dynamic as well.
Faraby Farid:
Exactly. Once you have building-level information feeding back through control systems, the network can respond more intelligently. You can operate at variable temperatures and make the whole thing more efficient.
Exactly. Once you have building-level information feeding back through control systems, the network can respond more intelligently. You can operate at variable temperatures and make the whole thing more efficient.
So district energy is not just about where the plant sits. It is also about how the whole system performs.
Roger Olsen:
Yes. If you can run chilled water at a slightly higher temperature, the chillers do not have to work so hard. If you can run heating water at a lower temperature, the heat generation becomes more efficient too.
Yes. If you can run chilled water at a slightly higher temperature, the chillers do not have to work so hard. If you can run heating water at a lower temperature, the heat generation becomes more efficient too.
It is all about not making the equipment work harder than it needs to. That is where a lot of the efficiency comes from.
Rebecca Stewart:
What is the biggest hurdle in making district energy work in practice?
What is the biggest hurdle in making district energy work in practice?
Faraby Farid:
The biggest hurdle is linking up multiple conversations and multiple project workstreams.
The biggest hurdle is linking up multiple conversations and multiple project workstreams.
One building may have a practical completion deadline next year, while the district energy network that could ultimately serve it may not be ready for several years. So the challenge is how you future-proof the building. You may still need to put some plant in at day one, but you want to design the building in a way that allows that plant to be removed or repurposed later when the wider network is in place.
That is one of the more complicated parts of the conversation, because it means coordinating across time as well as across assets.
Rebecca Stewart:
So the issue is not whether the idea works, but how you bridge the gap between what needs to be delivered now and what might be available later.
So the issue is not whether the idea works, but how you bridge the gap between what needs to be delivered now and what might be available later.
Faraby Farid:
Exactly. It is about sequencing and future-proofing.
Exactly. It is about sequencing and future-proofing.
Rebecca Stewart:
Do you find yourself waking up in the middle of the night thinking about how to persuade the different teams?
Do you find yourself waking up in the middle of the night thinking about how to persuade the different teams?
Faraby Farid:
I do not sleep very much anyway because I have young children, but yes, good solutions do often come at random moments.
I do not sleep very much anyway because I have young children, but yes, good solutions do often come at random moments.
Some of the best ideas come when you are not actively sitting at your desk trying to solve them.
Roger Olsen:
Yes, that’s very true. Sometimes the answer turns up when your mind is elsewhere.
Yes, that’s very true. Sometimes the answer turns up when your mind is elsewhere.
Faraby Farid:
One of the other reasons I am really pushing for district energy networks is that they can help reduce the urban heat island effect.
One of the other reasons I am really pushing for district energy networks is that they can help reduce the urban heat island effect.
If every building has plant on the roof, all of that plant is rejecting heat into the city. That makes the local environment hotter, which then in turn drives more cooling demand.
So if you can centralise and optimise that infrastructure, you can reduce some of that effect.
Roger Olsen:
And you can see this clearly on heat maps of London. The centre of London is significantly warmer than the parks and greener areas around it.
And you can see this clearly on heat maps of London. The centre of London is significantly warmer than the parks and greener areas around it.
The parks stand out because they are cooler, while the dense built-up areas are much hotter. It is a very visible reminder that buildings are not just isolated objects. They shape the city’s microclimate.
Rebecca Stewart:
Are there examples of other cities doing this well?
Are there examples of other cities doing this well?
Faraby Farid:
Yes. The closest example is Paris, which has one of the oldest district cooling networks in Europe. It is still running today and continues to evolve. During the Olympics they also used one of the aqua parks in a district heating and cooling strategy.
Yes. The closest example is Paris, which has one of the oldest district cooling networks in Europe. It is still running today and continues to evolve. During the Olympics they also used one of the aqua parks in a district heating and cooling strategy.
And across Europe more widely, a significant share of heating is already provided through district energy networks. The UK is much further behind, but this is one of the routes to decarbonisation that is increasingly being recognised at policy level.
Rebecca Stewart:
So planning and local authorities are starting to look at this more seriously.
So planning and local authorities are starting to look at this more seriously.
Faraby Farid:
Yes. It is becoming part of the conversation much more often.
Yes. It is becoming part of the conversation much more often.
Every local authority and planning authority should now be looking at this type of solution in a more structured way, because the future energy system is not going to be solved purely building by building.
Rebecca Stewart:
So we have looked at the fabric, the ventilation strategy and the wider energy source. Shall we move inside the building now?
So we have looked at the fabric, the ventilation strategy and the wider energy source. Shall we move inside the building now?
Roger Olsen:
Yes, let’s look at the inside.
Yes, let’s look at the inside.
If I sketch a section of the floor plate, one of the big challenges in heritage buildings is floor-to-ceiling height. A lot of these buildings have very limited space between the structural slab and the underside of the beams. And because many of them have changed use over time, the structure can be irregular. Some may have started life as separate buildings, then been stitched together. Others may have had different uses entirely, such as cinemas or theatres.
So one of the difficult aspects is figuring out how to make use of the internal space while still keeping it fit for purpose for the future.
Faraby Farid:
Exactly. Every building is different, and many of these West End buildings have had lots of work done to them over the years. Some have misaligned floors. Some have beams and services in odd places. Some have glazing that runs right down to the floor.
Exactly. Every building is different, and many of these West End buildings have had lots of work done to them over the years. Some have misaligned floors. Some have beams and services in odd places. Some have glazing that runs right down to the floor.
What that means is that space inside becomes absolutely critical. If you lose too much to services, the building can become much harder to let well.
Ideally, we are trying to keep clear heights in the range of around 2.7 to 2.9 metres where we can. But in many of these buildings, from the floor to the underside of the slab or beam, you do not even have that. So you are working in a very constrained envelope.
Rebecca Stewart:
And you cannot just start moving the structure around.
And you cannot just start moving the structure around.
Faraby Farid:
No. You can intervene structurally, but that comes with embodied carbon implications, heritage implications and cost.
No. You can intervene structurally, but that comes with embodied carbon implications, heritage implications and cost.
So again, the question becomes how to work with what is there rather than assuming you can simply reshape it.
Roger Olsen:
And those beams are there for a reason. They hold the building up. You are not going to be ringing up the original structural engineer and asking for the calculations. Even if you replaced them with modern steel, you would still have something projecting into the space.
And those beams are there for a reason. They hold the building up. You are not going to be ringing up the original structural engineer and asking for the calculations. Even if you replaced them with modern steel, you would still have something projecting into the space.
So you have to design around that reality.
Rebecca Stewart:
Which brings us to the systems people often default to.
Which brings us to the systems people often default to.
Faraby Farid:
Yes. The cheap and cheerful answer has often been VRF systems.
Yes. The cheap and cheerful answer has often been VRF systems.
That is one of the standard ways these buildings have been upgraded, often combined with secondary glazing. It is quick, it is familiar, it can help achieve tenant turnaround, and it is relatively cheap. But it also comes with problems.
Roger Olsen:
VRF means variable refrigerant flow. In practical terms, it is a refrigerant-based system using relatively small pipework but with refrigerant distributed through the building.
VRF means variable refrigerant flow. In practical terms, it is a refrigerant-based system using relatively small pipework but with refrigerant distributed through the building.
Faraby Farid:
And from a whole-life carbon perspective, I am not a big fan of it.
And from a whole-life carbon perspective, I am not a big fan of it.
You have refrigerant leakage over time, you have to keep refilling it, and it does not necessarily create the best quality of space. It is quick and relatively inexpensive, yes, but there are trade-offs in terms of comfort, carbon and long-term resilience.
Rebecca Stewart:
So if you have a tenant moving out and another moving in, that kind of system gives you speed.
So if you have a tenant moving out and another moving in, that kind of system gives you speed.
Faraby Farid:
Yes. That is one reason it has been used so much. If you are trying to turn around a building in six months, refrigerant-based systems are often seen as the easiest route.
Yes. That is one reason it has been used so much. If you are trying to turn around a building in six months, refrigerant-based systems are often seen as the easiest route.
But the wider question is whether that is still the right decision when you consider where regulation is going and how long the building needs to keep working.
Rebecca Stewart:
And the alternative people know is fan coil units.
And the alternative people know is fan coil units.
Faraby Farid:
Yes, but traditional fan coil units come with ductwork and larger boxes, and that is where the geometry problem comes back in.
Yes, but traditional fan coil units come with ductwork and larger boxes, and that is where the geometry problem comes back in.
If you already have less than 2.7 metres, once you add ductwork and associated services, you may end up down at 2.5 or even 2.4 metres. At that point, you are not delivering the quality of space you want.
So the real challenge is whether there is a water-based solution that can fit the same kind of constrained form factor as the systems people are used to using.
Roger Olsen:
Exactly. You want something without bulky ductwork, something that can sit between the beams and work with the space rather than overwhelming it.
Exactly. You want something without bulky ductwork, something that can sit between the beams and work with the space rather than overwhelming it.
Faraby Farid:
That is what we would propose wherever possible. If there is a solution that avoids ducts and still fits within the constrained floor-to-ceiling conditions, then that is the route we want to take.
That is what we would propose wherever possible. If there is a solution that avoids ducts and still fits within the constrained floor-to-ceiling conditions, then that is the route we want to take.
And because I set the technical standards for our developments, I have said there will be no gas, and refrigerant is only allowed where it can be clearly proven that there is no other viable way to turn the building around in time.
Rebecca Stewart:
And is that helped by F-Gas legislation?
And is that helped by F-Gas legislation?
Faraby Farid:
Yes, definitely. The phase-down of refrigerants is helping move the market away from the cheaper, older refrigerants.
Yes, definitely. The phase-down of refrigerants is helping move the market away from the cheaper, older refrigerants.
Newer refrigerants are much better from a global warming perspective, but they are also more costly. So once you get to that point, the cost comparison with a properly designed heat pump and water-based system starts to look very different. That is where cost parity starts to come into the conversation.
Rebecca Stewart:
So if we move on from system types, what about underfloor systems? They are often talked about as a lower-carbon solution.
So if we move on from system types, what about underfloor systems? They are often talked about as a lower-carbon solution.
Roger Olsen:
Underfloor can be a very good solution, but the challenge in these buildings is usually height. You often just do not have the available floor build-up to make it work properly.
Underfloor can be a very good solution, but the challenge in these buildings is usually height. You often just do not have the available floor build-up to make it work properly.
Faraby Farid:
Yes, if the space is there, underfloor is still a very good approach.
Yes, if the space is there, underfloor is still a very good approach.
From an embodied carbon perspective, it can work well. You are conditioning the space from a lower level, and as heat rises, it creates a more efficient distribution. But in many heritage buildings, the physical constraints make it difficult to implement.
Rebecca Stewart:
And are we seeing more heating or more cooling demand now?
And are we seeing more heating or more cooling demand now?
Faraby Farid:
Historically, it has been more heating. But as we improve the fabric and make buildings more airtight, cooling becomes more dominant.
Historically, it has been more heating. But as we improve the fabric and make buildings more airtight, cooling becomes more dominant.
When you combine that with climate change and the urban heat island effect, we are seeing a clear shift towards cooling demand increasing.
Rebecca Stewart:
So even though we are improving the building, the nature of the demand is changing.
So even though we are improving the building, the nature of the demand is changing.
Roger Olsen:
Yes, but it is still a good thing overall. Even if cooling demand increases, the total energy demand is still lower because the building is performing better.
Yes, but it is still a good thing overall. Even if cooling demand increases, the total energy demand is still lower because the building is performing better.
We are not making buildings worse — we are just changing the balance of where the energy is used.
Rebecca Stewart:
And we have all felt that shift. London in the summer has been quite uncomfortable recently.
And we have all felt that shift. London in the summer has been quite uncomfortable recently.
Faraby Farid:
Yes, and that is exactly the point. You can open windows, but when it is very hot outside, that does not necessarily help.
Yes, and that is exactly the point. You can open windows, but when it is very hot outside, that does not necessarily help.
So the question becomes how you design buildings that remain comfortable under those changing conditions.
Rebecca Stewart:
And how does that link to regulation?
And how does that link to regulation?
Faraby Farid:
Regulation is becoming a much stronger driver.
Regulation is becoming a much stronger driver.
EPC requirements are tightening, and buildings need to meet certain standards to remain lettable. If you have a poor EPC rating, you may not be able to lease the building at all.
So performance is no longer just a “nice to have” — it directly affects asset value.
Rebecca Stewart:
And comfort plays into that as well.
And comfort plays into that as well.
Faraby Farid:
Yes. Ultimately, you want to attract tenants who are willing to pay higher rents and who have fewer complaints.
Yes. Ultimately, you want to attract tenants who are willing to pay higher rents and who have fewer complaints.
Comfort is a big part of that. If people feel good in a space, they are more productive, they are more satisfied, and they are more likely to stay.
Rebecca Stewart:
So how do you balance all of this — performance, cost, comfort, and practicality?
So how do you balance all of this — performance, cost, comfort, and practicality?
Faraby Farid:
For me, it comes down to three things: feasibility, viability and desirability.
For me, it comes down to three things: feasibility, viability and desirability.
- Feasibility: Can you physically do it within the constraints of the building?
- Viability: Does it make sense commercially?
- Desirability: Does it create a space people actually want to use?
If you can achieve all three, then you are on the right track.
Roger Olsen:
And those three things are often in tension with each other. That is where the engineering and design judgement comes in.
And those three things are often in tension with each other. That is where the engineering and design judgement comes in.
Rebecca Stewart:
And I suppose that is where collaboration matters.
And I suppose that is where collaboration matters.
Faraby Farid:
Absolutely. These are not problems that can be solved in isolation.
Absolutely. These are not problems that can be solved in isolation.
You need developers, engineers, architects and contractors all working together. And you need a willingness to try different approaches.
The industry can be quite risk-averse, but if we want to make progress, we have to be prepared to test new ideas and learn from them.
Rebecca Stewart:
So if you were to summarise the biggest takeaway from this conversation, what would it be?
So if you were to summarise the biggest takeaway from this conversation, what would it be?
Faraby Farid:
Start with the building.
Start with the building.
Understand the fabric, reduce the demand, and then design the systems around that. If you get that sequence right, everything else becomes easier.
Roger Olsen:
Yes, I would agree with that. Look at the building first, not the system.
Yes, I would agree with that. Look at the building first, not the system.
Rebecca Stewart:
That feels like a good place to end.
That feels like a good place to end.
Thank you both for joining me. It has been a fascinating conversation, and I think a very practical one for anyone working with existing buildings.
And thank you to our listeners for tuning in. We do recommend that you watch this episode as well, as we have been sketching throughout.